The inventors herein have recognized that the number of cycles completed by an engine during an engine shutdown can affect emissions on subsequent engine starts. Specifically, after fuel injection is stopped, the engine may continue to rotate, thus pumping lean gasses to the catalyst thereby increasing its oxidation state. Then, during subsequent restarts, the oxidized catalyst may perform less efficiently.
In one example, this can be addressed by a method for discontinuing combustion in a cylinder of an internal combustion engine having an intake manifold and an emission control device coupled downstream of thereof, where the cylinder has at least one electrically actuated valve, the method comprising: during engine shut-off, holding the at least one electrically actuated valve closed for at least a cycle of the cylinder to reduce a flow of gasses from the engine to the emission control device.
It this way, it may be possible to reduce the amount of gasses pumped through the catalyst. For example, less excess air may be pumped through the catalyst thereby reducing emissions on subsequent engine starts, such as hot restarts. Further, other advantages may be obtained as discussed in detail below.
Alternatively, the inventors herein have also recognized that in some examples engine braking can be reduced while at the same time still reducing flow through the engine so that more energy may be recovered, such as in a hybrid vehicle configuration. As such, operation as described above may have still other advantages.